This invention relates to antenna systems, and more particularly to a space-fed, polarization twist, E-scan phased array antenna incorporating ortho-linear phased array elements and micro-electro-mechanical-switch (MEMS) phase shifters that can be provided a monolithic microwave integrated circuit (MMIC) wafer.
Missile defense radar systems that require high scan rates would ideally incorporate electronically scanned (xe2x80x9cE-scanxe2x80x9d) antennas rather than mechanically scanned antennas. However, most of past and presently implemented radar systems have incorporated mechanically scanned antennas instead of E-scan phased array antennas. The major reason for this is the development and production cost of past and present E-scan phased array antennas, which are significantly more costly to manufacture than mechanically scanned antennas. Another reason is that past and presently implemented E-scan phased array antennas are less efficient than mechanically scanned antennas because conventional E-scan phase shifters have high insertion loss, especially at millimeter wave frequencies. Conventional corporate-fed E-scan phased arrays also require complex feed networks, as well as having high insertion losses, especially for a large millimeter wave, E-scan phased arrays. These conventional corporate-fed E-scan phased array antennas also require a large number of phase shifter bits to produce low phase quantization sidelobes.
Conventional space-fed E-scan phased array antennas also have significant drawbacks. The space-fed E-scan phased arrays occupy a large volume in back of the array aperture that reduces valuable space required for other electronics.
Conventional E-scan reflector phased arrays have a large aperture blockage caused by the feed and sub-reflector, which produces undesired high antenna pattern sidelobes. In addition, the radiating elements of such arrays are structurally complex, and each element module consists of numerous independent parts requiring multilayered and multi-connection circuit construction. At the millimeter wave frequency, the fabrication tolerance requirements of individual parts is extremely exacting, which also significantly increases the fabrication cost of such arrays.
It is therefore a principal object of the present invention to provide a low cost, E-scan phased array antenna which provides improved performance at significantly reduced manufacturing costs to thereby enable its use in broad applications involving radar systems.
It is still another object of the present invention to provide a low cost, E-scan phased array antenna which does not require a complex feed network having high insertion losses, and which therefore is particularly well suited for large millimeter wave E-scan phased arrays.
It is still another object of the present invention to provide a low cost E-scan phased array antenna which requires fewer phase shifter bits for each array element to produce low antenna sidelobes.
The above and other objects are met by a polarization twist, planar, space-fed E-scan phased array antenna in accordance with preferred embodiments of the present invention. The antenna comprises a polarization twist Cassegrain space-feed architecture and a plurality of ortho-linear polarization array elements and electronic phase shifters. In one preferred embodiment, the electronic phase shifters comprise micro-electro-mechanical-switches (MEMS) phase shifters. In various preferred embodiments, the phased array elements comprise ortho-linear polarization elements, microstrip patches, dipoles, or slots, but are not limited to these embodiments. The specific types of ortho-linear polarization phased array elements, the relative placement of phased array elements and phase shifters may all vary to meet specific design criteria.
Each phased array element is formed on a monolithic microwave integrated circuit (MMIC) substrate. The simplified construction and electrical connections provided by the phased array elements permit several thousand phased array elements to be formed on one or more layers of the MMIC substrate. The antenna of the present invention reduces the number of phase shifter bits on each phased array element to enable all, or substantially all, of the necessary components of each phased array element (i.e., radiating element, phased shifters and control circuits) to be fit into a planar unit cell area. This makes the antenna of the present invention significantly more structurally simple than previously developed E-scan phased array antennas. With fewer phase shifter bits per array element, processing yields can be significantly increased, thus enabling the production of E-scan, phased array antennas to be employed in missile defense radar systems and other applications where the E-scan phased array antenna would have been too costly to employ.